Police are now investigating if a train collision in Chicago was caused by someone hijacking a train, CBS Chicago reports.

Officials told ABC 7 that a westbound train and an eastbound train were on the same track and collided near Harlem Avenue and the Eisenhower Expressway at around 8 a.m. The Chicago Sun-Times reports that the westbound train was at stopped at the Harlem Station when the accident happened. It is not clear why the trains were on the same track.

The injury count has been fluctuating since the news broke, and now stands at 33, according to NBC Chicago. Those people were transported to area hospitals and their injuries are not thought to be life-threatening.

Suspicions about a hijacking surfaced as the train that caused the crash was only four cars long, shorter than those used in rush hour. Forest Park Mayor Anthony Calderone told CBS Chicago that no one was at the controls of the train when it crashed.

A locomotive engineer who witnessed the crash told NBC Chicago that it appeared the train blew threw a signal because she heard beeping. She told the news station: “When you hear those beepings it’s warning you that there is an obstruction in front of you and you need to stop.”

The CTA’s Twitter feed says that service between Forest Park and Austin has been suspended and that shuttle buses are running as a replacement. Ambulances were called to the scene to transport people to area hospitals.